Modifying the Cathode Catalyst Layer in PEM Fuel Cells with Ionic Liquids for Improved Oxygen Reduction Reaction

Abstract

Increasing the accessibility of green, affordable hydrogen and reducing the cost of polymer electrolyte membrane fuel cells (PEMFC) devices are critical to the widespread commercialization of hydrogen powered fuel cells. The high cost of PEMFCs is in part due to the high Pt leadings in the cathode catalyst layer (CCL) to compensate for kinetic and transport losses during the sluggish oxygen reduction reaction. Therefore, substantial research efforts have been focused on modifying the CCL and its constituent components to achieve cost parity with other advanced energy technologies, particularly in the transportation sector.Hydrophobic ionic liquids (ILs) have been used as interfacial additives for oxygen reduction reaction (ORR) electrocatalysts, demonstrating enhanced catalyst activity and durability.1,2 However, incorporating ILs or IL-modified catalysts into the electrodes of a PEMFC membrane electrode assembly (MEA) has proven to be challenging. To address this limitation, we developed a new ionomer chemistry with orthogonal properties of protonic conductivity and ionic liquid functionality: sulfonated poly(ionic liquid) block copolymers (S-PILBCPs). The new ionomer in the Pt/C CCLs yields a two-fold improvement in the kinetic activity, both in the half-cell and MEA. Furthermore, a Nafion/S-PILBCP composite ionomer substantially improves the high current density performance as well.3 In this work, we use rotating disk electrode (RDE) techniques to electrochemically characterize the Pt/S-PILBCP interface. Our analysis demonstrates the promise and utility of hydrocarbon-based poly(IL) ionomers over the traditional ionomer-Nafion and also provides important insights about observed MEA performance enhancements.